The present invention relates to the field of radio frequency (RF) antenna systems. More specifically, the present invention relates to methods and structures for concealing RF antenna systems.
Cellular communications networks utilize radio frequency (RF) antenna systems at xe2x80x9ccell sitesxe2x80x9d to transmit and receive RF signals. Cell sites are typically spaced from three to eight miles apart to achieve acceptable results. Consequently, a large metropolitan area can include hundreds of individual sites to insure thorough coverage. RF antenna systems are typically attached to the sides or rooftops of buildings, or are mounted on new or existing tower structures. The RF antenna systems are generally enclosed in housings to prevent the antennas from being damaged by the environment or mishandling. These housings often have the unsightly appearance of large boxes on sides of buildings and rooftops, or hanging from towers. To compound the problem, an array of antennas of varying sizes and shapes for several different systems are often found on a common tower.
The general public and the municipal zoning boards are becoming increasingly and vehemently intolerant of RF antenna systems and antenna towers in their communities. This intolerance is due to the visual undesirability of the systems and the perception that the presence of the antenna systems and towers has an adverse effect on local property values. These opinions increase the resistance to building additional sites within communities to provide service to the ever rising number of wireless communications subscribers.
The preferred locations for placement of RF antenna systems are typically the tallest available locations relative to the surrounding terrain within the intended coverage area. The tallest available location ensures that the line of sight will most likely be free of obstructions that may reflect electromagnetic waves from the direction of the desired coverage. Antennas mounted on the sides or roofs of buildings or mounted on towers atop the most prominent, visible locations within the surrounding landscape greatly exacerbates the aesthetics problem.
To reduce the objectionable aesthetics of RF antenna systems, concealment strategies have been attempted to make them blend within the existing architecture of a building or a location. Such concealment attempts include hiding antennas behind xe2x80x9cscreenxe2x80x9d structures and within church steeples and bell towers, mounting antennas on streetlamps, decorative towers, and utility poles, disguising conventional antennas as flagpoles and trees, and so forth. Such strategies have achieved only limited success in terms of aesthetics because disguises often do not appear natural and because of the limited availability of existing structures onto which antennas may be mounted.
In addition to aesthetic effectiveness, the successful concealment of RF antenna systems entails the consideration of a number of constraints when designing, fabricating, and mounting antenna screen structures. These constraints include, for example, the structural soundness within the requirements of the local and/or regional building codes, the introduction of minimal detrimental effects on the RF signal, the ability to resist degradation from environmental effects, and the capability for relatively quick installation. Ideally, all of these constraints should be satisfied, or balanced, while maintaining economic viability.
One typical concealment approach is to use multiple common structural elements made from fiber reinforced plastic (FRP), such as, angle, channel, tubing, I-beams, and plates. Using these elements, a screen structure is designed and assembled as though the structural elements were metal pieces. Unfortunately, such a design requires hundreds, and even thousands of fasteners, to hold it together, thus increasing the complexity and cost of assembly.
Another concealment approach is a hybrid of the multiple elements approach. This hybrid approach reduces some of the complexity of the multiple elements approach and improves the aesthetics by making modular wall panels arranged in long rows. This hybrid approach uses a minimal amount of custom tooling (molds), thus decreasing the cost of the screen structures over the multiple elements approach.
In order to enhance customer satisfaction, RF signal degradation in the cellular network should desirably be kept at a minimum. The placement of any matter, including screen structures, will present some degree of adverse effect on RF signals. A predominant factor that affects RF signals is the cross-sectional mass of the material. That is, the greater the mass between an antenna and a receiver, the greater the effect on the signal. This problem of cross-sectional mass is exacerbated when beams and columns that support the screen structure are in the signal path. A horizontal beam in the signal path can introduce a small signal disturbance, generally in the form of a phase-shift. In contrast, vertical columns (and diagonal brackets) in the signal path introduce significant RF attenuation and phase shift. The multiple element concealment approach and the hybrid approach can suffer from RF degradation due to the beams and columns in the signal path that are used to fabricate the screen structures.
Radio system planners are typically required to perform a structural analysis of a proposed configuration of an antenna screen structure to evaluate the stresses and strains to which the proposed screen structure will or might be subjected. The analysis of a multiple element construct of a structure typically employs familiar conventions used in the analysis of structures of metal, wood, concrete, and so forth. Unfortunately, these familiar conventions do not capitalize on the properties of the materials used to manufacture RF transparent screen structures. In addition, a multiple element construct of a screen structure, such as the multiple element and the hybrid concealment approaches may undesirably complicate the structural analysis, thus increasing the time and costs associated with performing such an analysis. Furthermore, changes to the configuration of the proposed screen structure that demand further structural analysis again results in adverse time and cost affects.
Accordingly, it is an advantage of the present invention that a method for concealing a cell site radio frequency (RF) antenna system is provided.
It is another advantage of the present invention that a computer-based method is provided that evaluates a configuration of an antenna screen structure and rapidly assesses structural integrity and cost information.
Yet another advantage of the present invention is that a method is provided that balances aesthetic effectiveness, RF degradation potential, structural integrity, and cost considerations in the design, fabrication, and installation of antenna screen structures.
The above and other advantages of the present invention are carried out in one form by a method of concealing a cell site radio frequency (RF) antenna at a location. The method calls for generating a configuration of an antenna screen structure to determine geometrical parameters of the configuration. A set of instructions are executed on a processor to evaluate the configuration of the antenna screen structure. The instructions direct the processor to perform operations that include obtaining structural parameters of the configuration, receiving a wind load value for the location, and computing a maximum deflection value of the configuration in response to the geometrical parameters, the structural parameters, and the wind load value. When the maximum deflection value is less than a deflection limit value, the method determines that the configuration of the antenna screen structure has acceptable structural integrity. The configuration of the antenna screen structure is fabricated to imitate an appearance of a structure at the location, and the antenna screen structure and the cell site RF antenna are mounted at the location so that the cell site RF antenna is hidden from an observer.
The above and other advantages of the present invention are carried out in another form by a computer-based method for evaluating a configuration of an antenna screen structure formed to conceal a cell site radio frequency (RF) antenna at a location. The computer-based method calls for defining geometrical parameters of the configuration, obtaining structural parameters of the configuration, and receiving a wind load value for the location. A maximum deflection value of the configuration is computed in response to the geometrical parameters, the structural parameters, and the wind load value. The maximum deflection value is compared to a deflection limit value, and the configuration of the antenna screen structure is determined to have acceptable structural integrity when the maximum deflection value is less than the deflection limit value.